So one night i parked my car and the next morning it was dead. It cranked like a half then 1/4 then nothing barely enough for lights on dash. I boosted it and it fired right up ran fine. Turned it off. After 1 min fired right up again. Went to Safeway came out fired right up. Came home left it for about 3-4 hours dead. Boosted it again fired right up. Went to Canadian tire for new battery came out fired right up. Each time when the car is off i can hear a buzzing or groaning sound coming from the battery area but im sure its not coming from the battery its self. The alternator is brand new and its charging over 15v never had any dimming lights on dash or headlights. Now that i hooked up the new battery it made the sound soon as i hooked it up so i left it unhooked to prevent drain if there was any. The next morning i went out and hooked it up there was no sound but after about 3 min it started like ... . .. ............ then stopped again. Sound is only there when car is off and it has been cold out. We had a few days of -40 then it has been +3 up till this problem.

Ive talked to a few people and they said it could be the regulator but i searched it up and there was no light issues nor indicators of that and there was a small amount of corrosion on the neg post but i cleaned that off completely before i removed the old battery. Now my issue is was it the old battery? Pretty new id say a year or 2 or is its this odd buzzing that i don't remember ever hearing before? I dont have the money to replace the mysterious part if that's the cause so i dont wanna take it in right away and i was gonna borrow a voltmeter and such in the next few days to do further testing. Any input from experience or otherwise appreciated.

2 Answers
2

First. Car batteries can be overcharged. When they are, they will 'gas' or 'boil,' which could be the noise you describe. This will continue for a few minutes after the car is turned off. You could easily verify if this is it by waiting for it to occur, and then disconnect the battery. If the car is charging at more than 14.5v while running, and the noise continues while the car is off and the battery is disconnected, it's likely that this is what's happening. Overcharging damages the battery, and reduces its capacity.

The culprit, if overcharging is the problem, is definitely the alternator regulator or another part of the alternator's voltage sense circuit. I'd be especially suspicious if this problem has cropped up after the alternator was replaced, as it's easily possible to have gotten a defective replacement part.

Second. If the noise stops immediately when you disconnect a battery terminal, then it's probably something that's staying on while the key's off and is gradually draining the battery. This can be found as described by 'user1126070'. Instead of a multimeter I have found that a simple test light works for this. I'll rewrite the procedure in case its clearer:

-When the battery is well charged, disconnect one battery lead from its battery post. Leave the other one connected.

-Connect one wire from your test light to the battery post, and the other wire to the removed battery clamp.

-In a circumstance when there is something using power from the battery, the light will illuminate (sometimes dimly). Verify that the test is valid by deliberately turning on something in the car and see if the light illuminates. Then make sure everything is off, doors closed, etc. as it would be when you park the car. If you still have a load drawing current through the light and illuminating it, you can isolate where it is in the car's wiring by removing fuses one at a time.

Finally,

Third. I can imagine a situation where both these above scenarios are relevant. An alternator's voltage regulator is designed to send power from the battery into the alternator's rotor. It controls how much voltage goes in to determine how much energy the alternator generates. IF the regulator has failed in a way that causes it to over-charge, it could be that it never shuts off, or always uses battery current to energize the rotor even when the car is stopped. You might not be able to isolate this possibility by pulling fuses; instead, you'd have to actually disconnect the wiring from the alternator.